CT imaging systems can be used for checking blood vessels, especially for detecting narrowing (stenosis) in the blood vessels. FIG. 1 is a schematic illustration of a display showing two blood vessel views, a view 100 showing a blood vessel 102 and a view 122, a slice generally perpendicular to vessel 102, along a plane marked as 120. It should be noted that in most situations, vessel 102 will not lie uniformly in one plane. It is desirable to determine a centerline 108 of vessel 102, so that slices 122 can be made perpendicular thereto and allowing various views along and of the blood vessel. For example, the vessel may be checked for narrowing by providing a series of slices perpendicular to the blood vessel or the vessel may be spread out into a flat image, for inspecting its wall.
An exemplary current practice is to have a user mark multiple points (e.g., 16-32 points) along an estimated centerline 108 and then connect them with straight lines or use various algorithmic methods to obtain a more exact determination of the centerline.
It should be noted that centerline determination is generally not a trivial task. In many cases parts of the blood vessel are missing, have non-uniform CT numbers (Hounsfield numbers) and/or the edges of the blood vessels are not clear. Exemplary reasons for this are:
(a) Even if the blood vessel is imaged using a contrast material, this material may not be uniformly distributed along the blood vessel.
(b) Partial volume effects, especially near bones.
(c) Nearby tissue with similar absorption (e.g., cortical bone, marrow and kidney tissue). For example, a boundary 118 might not be visible next to a bone 116.
(d) Narrowing, splitting and/or other geometrical properties of vessels.
(e) Some vessels contain stents.
(f) Nearby vessels may appear to meet and merge and then diverge.
(g) Various effects may cause a vessel to appear to include loops.
(h) An incorrect centerline can cause the appearance of a narrowing while viewing the vessel.
(i) An unsmooth centerline can cause difficulty in viewing and/or understanding the entire blood vessel.
(j) Occlusions.
PCT publication WO 2004/086310, the disclosure of which is incorporated herein by reference, describes a method of curvilinear modeling. In this publication, a minimum cost path is converted into a curvilinear model of a tubular organ, by resampling the data around the minimal cost path into a transformed data domain and then further processing in that domain.